The present invention relates to power supplies in general, and in particular to a line-frequency switching series-pass transistor stage in a power supply.
There are many types of power supplies for providing stable, regulated DC voltages to operate electronic equipment and circuits therein. Conventional linear supplies, which typically comprise an electronically regulated pass transistor coupled to the output of a rectifier and filter network, are designed for worst-case low power line operation and dissipate unused power in the form of heat. That is, the line voltage range may be from 90 volts AC to 130 volts AC, and to maintain a constant output DC voltage over that range, the pass transistor must drop the unused voltage generated by the rectifier. Moreover, since the pass transistor conducts over the full line-voltage cycle, large heatsinks may be required to dissipate the unused power.
Recent trends in power supply design have been away from linear types to switching types because switching power supplies have higher conversion efficiency, less bulk, and dissipate less energy in the form of heat. Switching power supplies, however, typically are considerably more complex than linear supplies, and operate at fairly high frequencies, e.g., from several kilohertz to several megahertz, and as a consequence, generate considerable noise and extraneous radiant energy which requires additional filtering and shielding.